Method for anodizing aluminum

Abstract

Method of anodizing an aluminum workpiece wherein the workpiece and belt of cloth fabric is moved through a contact zone over an electrically conductive rigid backing member. The relative speeds of the workpiece and the belt are adjusted so that the belt is caused to wipe across the surface of the workpiece. Anodizing solution is applied to the workpiece in the contact zone and a direct electric potential is applied with the backing member as the cathode and the workpiece as the anode.

I claim: 
     
       1. A method of anodizing an aluminum workpiece comprising the steps of: (a) moving the workpiece and a belt of cloth fabric through a contact zone over an electrically conductive rigid backing member;   (b) adjusting the relative speeds of the workpiece and the belt so that the belt is caused to wipe across the surface of the workpiece;   (c) supplying an anodizing solution to the workpiece in the contact zone, whereby the wiping action of the belt continuously removes reaction products from the workpiece surface and exposes fresh surface area to the solution; and   (d) applying a direct electric potential with the backing member as the cathode and the workpiece as the anode.   
     
     
       2. The product produced by the process of claim 1. 
     
     
       3. The method of claim 1 wherein said anodizing solution is an aqueous solution of an acid selected from sulfuric, oxalic, and mixtures thereof. 
     
     
       4. A method of anodizing aluminum strip comprising the steps of: (a) moving the strip and an endless belt loop of cloth fabric through a contact zone over a perforated, electrically conductive backing member;   (b) applying an anodizing solution to the fabric belt;   (c) adjusting the relative speeds of the belt and strip so that the belt is caused to wipe continuously across the strip surface to remove reaction products and expose fresh surface area to the solution;   (d) cleaning the belt subsequent to the contact zone and reapplying fresh anodizing solution to the cleansed belt; and   (e) applying a direct electric potential with the backing member as the cathode and the strip as the anode.   
     
     
       5. The method of claim 4 wherein the anodizing solution comprises an aqueous sulfuric acid solution of from about 10% to about 25% by weight sulfuric acid. 
     
     
       6. The method of claim 4 wherein the strip is a lithographic platestock which is grained prior to being anodized. 
     
     
       7. The product produced by the process of claim 6 or claim 4.